The investigations were conducted at Bangalore, India. A total of 627 periodic mass flights (PMFs) were observed during 10 successive days from 26 colonies of Apis dorsata at a polytechnic building site and 82 colonies at a banyan tree site at the Agricultural University 15 km away. PMF activities performed by particular A. dorsata populations were similar in successive days at a particular site. However, at the polytechnic site, where favourable environmental conditions prevailed, 84.3% of colonies performed 2.3 PMFs per colony per day, while at the banyan tree site, with less favourable conditions, only 11.3% of colonies performed 0.11 flights. We suggest that PMF activities depend in part upon the amount of unsealed brood. Individual colonies performed 0–5 PMFs in successive days. Low numbers of 1–2 PMF per day were preceded by high numbers of 4–5 flights the following day. Similarly, PMFs of low intensity were followed by flights of high intensity. However, two- or three-day cycles of similar activities were also observed. Surprisingly, no correlation was found between the sizes of the combs and the number and intensity of PMFs. We explain this by the fact that a similar amount of unsealed brood was present in combs of different sizes.